Bores are common mechanical structures found on a large number of mechanical equipment, such as excavators or the like. Bores may be used for different purposes, for instance to receive a shaft or a pin to form a hinge. Even the cylinders of an engine may be considered as bores.
It is widely known that bores tend to get worn and damaged during their normal use or when subjected to a particularly intensive effort. Cracks may form on the sidewall of the bore, which may compromise the structural integrity of the equipment or of part of the equipment.
Various techniques, including boring and welding, are usually available to repair the bore. To perform these operations, a portable boring-welding machine may be used. This machine allows a user to alternatively perform boring and welding operations on the same workpiece. This type of machine is particularly useful to repair bores on large pieces of equipment which would be difficult or even impossible to move and install on a standard machine tool, because the portable boring-welding machine may be mounted directly on the piece to repair.
A portable boring-welding machine typically comprises a shaft which axially engages the bore and a tool mounted to the shaft for performing the boring and/or welding operation. A feed mechanism may also be provided to move the shaft axially along a certain length of the inner wall of the bore. During operation of the machine, the shaft is also rotated to allow a tool to move in a circular path against the inner wall.
However, the shaft is usually not rotated at the same speed during welding and during boring.
During boring, the shaft is rotated at a relatively high speed and with a certain torque in order to enable a boring tool to penetrate the inner wall of the bore. To provide the desired speed and torque, a hydraulic motor is typically used to rotate the shaft during boring.
During welding, the shaft is rotated at a relatively low speed and requires little, if any, torque, but usually requires the rotation speed of the shaft to be set with relatively higher precision than during boring.
To rotate the shaft at this lower speed, a speed reducer may be used. Example of a product on the market using such a technology includes the Portable Line Boring Machine MKIII™ manufactured by Hoffman Engineering Pty Ltd. (Perth, Australia).
Unfortunately, this increases the torque provided by the shaft, and this relatively high torque may damage the welding tool when performing a welding operation. A torque limiter may further be coupled to the speed reducer in order to limit the torque provided to the shaft, but this configuration does not eliminate the possibility that the limiter may fail during operation and damage the machine and/or the bore. Furthermore, the addition of two devices, namely a speed reducer and a torque limiter, would further increase the weight and complexity of the machine, which would then become costlier to manufacture and operate.
It has also been suggested to use a separate motor, such as an electric motor, which may allow the shaft to be rotated at a lower speed during welding without providing unnecessary torque. Examples of products on the market using such technology includes the WS™ series manufactured by Sir Meccanica S.p.A. Italia (Cantazaro, Italy); Elsa™ and the Supercombinata series sold by Penouest (France).
Unfortunately, this configuration implies providing an additional motor on the machine, which may also make the portable boring-welding machine more complex and thus costlier to manufacture and operate.
There is therefore the need for a device which would overcome at least one of the above-identified drawbacks.
Features of the invention will be apparent from review of the disclosure, drawings and description of the invention below.